Are you looking for a synthesizer to learn Sound Synthesis and have some great sounds? Charlatan of Blaukraut Engineering is the one to check out.

The TAL U-No-62 is a polyphonic virtual analogue synth with a unique filter sound. A Roland JUNO 60 soundalike.

The Steinberg VB-1 is a small and easy to use virtual bass plugin and is a very simple plugin with some surprisingly useful sounds. 

The Fullbucket MPS is a surprisingly easy to work with synthesizer, it aims to create sounds fast and easy using a small intuitive set of parameters.